Control system



- April-28, 1936. E. H. BRISTOL I R 19,944

CONTROL SYSTEM Original F il d Jan. 24; 1931 I I I 'lI/l/IIIII/ VI/II/I/l/IIIIII:YIIIIII/III/Il Reissued Apr. 28, 1936 CONTROL SYSTEM new 11. Bristol, Foxboro, Mass., assignor to n.

' Foxboro Company, Foxboro, Masa, a corporation of Massachusetts Origin 8| No. 1,911,092, dated my 4.19%, Serial- No. 510,926; January 24, 1931. Application for reissue June 2a, 1935, Serial No. 29,105

1 Claims. (01.137-139) This invention relates to control systems which embody a valve or similar mechanism operated by a servo-motor, and the object is to provide improvements in such a system whereby more uniform results may be attained and the eflect of mechanical factors, which in previous constructions have adversely influenced the accurate functioning oi the mechanism, may be obviated. My invention may be well understood by reference to the tollowing'descrlption of an illustrative embodiment thereof taken in connection with the accompanying drawing, wherein I have shown diagrammatically and partly in section a system oi the type wherein a-valve is operated by a pneumatic motor thermostatically controlled.

Referring to the. drawing, I have there shown a valve 3 adapted to control the; flow of some fluid, such as steam, through the pipe- 5, the valve being operated by a" diaphragm motor I. The valve herein shown is 01' the type which is opened by pressure in the motor and closed by the spring I when the pressure is relieved. It is adapted to float in partly open positions between open and closed positions. Friction on the valve {stem resists movement of the valve and in prior constructions in which the pressure admitted to the motor was proportional to temperature or some other controlling variable, the valve might take diflerent positions accordingly as whether the pressure was increasing to a certain value or decreasing. In accordance with my invention I provide a construction wherein substantially identical positions of the valve may be obtained when desired regardless of the pressure needed to move the valve.

The system shown in the drawing may be subposed to be utilized to maintain a constant temperature in the interior or tank I i as measured by a suitable thermometric-device including the bulb It in the tank communicating with a suitable responsive device, as, for instance, the helical Bourdon tube I! like that shown in the patent to Bristol 1,195,334, dated August 22, 1916. The

. responsive device ll may operate one-element 01' v a control couple such as the valve or flapper" ll which cooperates with acompanion element and takes the form of a ported member .or .nozzle" l9 4 which, through the diaphragms 2| and the hollow stem 33 ofadoublevalve 25, provides a communication to atmosphere 101' the interior 01' a .'control head 21 ot the supplyand waste type.

This mechanism is in principle like that described in the patent to Johnson 542,733, dated July 16,

1896, and in detailed construction may be and preferablyissimilar to that shown in the patent v to Dixon 1,582,868, dated April 27, 1926, while the flapper is preferably of the throttling type dis-- closed in my Patent 1,641,744, dated Sept. 6, 1927. The valve 25 in the position shown controls the flow of pressure fluid from a supply line 28 through branch 3| to pipe 33. Hitherto it has been customary to permit the air to flow directly to the servo-motor operating the valve. Herein on the contrary pipe 33 leads to a motor 35, herein shown as a helical Bourdon tube or pressure gage adapted to be distorted more or less as the internal pressure varies and carrying on its free end an element of a control couple in the form of a valveor flapper 31. The cooperating element consisting of a ported member or nozzle 39 is caused to move proportionately to the movements of the valve 3 and herein is shown as mounted directly thereon to reciprocate therewith. The ported member may be in communi! cation through the flexible coil 4|, which serves to permit it to move freely, through diaphragms 43- and the hollow stem 45 01' a double valve 41 with the interior of control head 49 of the supply and waste type which is interposed between the supply line 29 for air under pressure and conduit 5| leading to the motor I.

The parts being in the position shown, flapper II is raised from its seat on nozzle i9 and. air entering the control head at pipe 3| bleeds through the hollow stem 33 and exhauststo at- .mosphere through the nozzle. -Diaphragms 2| are collapsed, valve 25 is in the position shown and air flows through pipe 33 to the motor tube 35, which, being distended, moves flapper 31 downwardly causing it to tend to move away from the ported member 39. Similarly air enthe responsive element It is operated and permits valve or flapper IT to start to-close over the port I! causing pressure to build up in diaphrasms 2| thereby causing the-valve to start shifting to the right, decreasing communication between 33 and 3| and permitting motor 35 to exhaust to the atmosphere through pipe 33 and the port opened at the left or the valve 25. ,Flapper 3I.therei'ore motes toward ported member or nozzle 38, building up pressurein diaphragms 43 and causing valve 41 to shift-toward the left tering control head 49 from the main line bleeds phragm motor I and permitting thelatter to ex- 7 haustto the atmosphere through pipe SI and theport opened by valve 41- at its! right. This begins releasing valve I to. the action 01 the spring 9 which commences closing the valve. As

the valve moving in its closing movement starts to move nozzle 18 awayirom valve or flapper 31 the couple changes the position of .thevalve 41 which tends to hold the nozzle 39 and valve 3: in the position corresponding to thepositionassumedbyflapperfl. V

It will thus 'be seen that the tiiermornetridevice II and control head 21 withits control couple. and II establish a certain pressure in motortuhe II cm'responding'to a given temperature and that to anypr'essure in motor tube I5 therewili correspondaposition'oi nozzle 39 andwith itofthevalveandi stemithispositionbeingbroughtaboutbyapressureapplied throughcontrolheadfltodiaphragmmotor whichpressm'einthemotorlmayormaynot 'beidentlcalwlththepmssureinfl A'gradnalchangeinpressmeinmotortiis attained whenflapperl'lis or the throttling type described inniy Patent 1,641,744above referred to. lalternatively or in coniunction therewith I may utilize arstriction il-in pipe 33' which permitsonlyaslowmeofairtherethrough.

Ipreiertoprovidei'oragradualflowoi'enersytoandi'romthevalveoperatingmotor1in responsetoagovernimactiondthemechanism,

. and herdn .I' have shown pipe ll as'provided Q .tion 53 corrects this.

withthierestrictioniliordampingtheflmoi strlctionthemotormaytendtopulsatebecause oitheiactfl'iattheresistonce'toimflslmovementolthevalveisgreat'srthantheslidingfric 'tionofthevalvestemoncethemotlon'has-begunhlnmanycasespulsationisundesirahlei Furthermore, in caseswhere'the couple separates completely itispossihlethatasudden impulseotairundermllpressuremaybeap-l plied,tending toopenthevalve,amibdorethis' canbereleased.the valvemayhave movedbe-' Theuseotarestrlc yond its desired position.

While]: have for purposes of clearness and by way or illustration described a pneumatically operated valve thermostatically controlled, I am aware that the invention may be embodied in other specific forms without departins from the spirit or essential attributes thereof, and I therefore desire the present embodiment to be consideredinallrespectsasillustrativeandnot reflmdtothemotoreanwlsimavalvemechanism strictive; reference being had tothe appended claimsratherthantothei'oregoina description toindicatetheacopeditheinvenflon. Iclaim: Llneomhinationwithavalvehavlngapressure-fluid-cperated motor for operating the ot the supply and waste typa-a emtrolpouple theretomtherelafiveapproachandrecessimot theelemenuotwhichgovernthesaidvalve mechanismone element ot-which couple is moved proportionately to movement of said.

valve, the relative position oi said elements being further cook-oiled by a pressure-fluid-operated device, controlling flow oi fluid to said device comprising a valve mechanism of the supply and waste type and a control. couple, and means responsive to the fluctuations of a elements thereof.

, 19,9 reducingthe supply oi' pressure fluid to diavariable condition for relatively positioning the 2. ,In combination with a motor-operated valve comprising a control couple, the" relative appreach and recession oi the elements of which govern the supply 0! energy to the motor. one

element'oi the couple moving proportionately tothe valve, a tube subject to distorting internal pressure connected to one or said elements for further controlling the relative positions of the same, and means to admit pressure fluid to said tube comprising a fluid pressure control mechanism of the supply and waste valve type including a control couple, one element of which atiordsa porttoaflnosphereandthe otheravalve for saidport,the relativeappmachandreceasion otsaidelementsgoverningthepresaureinthe csa variable for the elementsoi'saidseeondcouple.

3. Incornbinationvlrithaanotor-operatedvalve comprisingacontroleolmletherelativeapprooch andrecemionott-heelementsotwhichgovernthe supply at energy to'the motor, one elemental thecouplemovingpmpwtlonatelytothevalma pausme-flnid-operated motor for moving the other elunent, and means controlling the-flow oifluidtheretocomprisingavalvemechanlsmot couplethm-eior,therelativeapproachandrecesaionottho elementsdwhichgovern'thesaidmechanisnand meamrsponsivetothefluctuatiomotavu'lable condition for reiativelypositiming theeiemenfl tmreoi'. a

4.1ncmnblhaiionwith-avalvehavingapressure-fluid-operated motori'or operating the some, a emdnitior the fluid having'a restriction for dampemngthemwtoandn'omthemotm'meall.

conduit comprising a valve mechanism otthe sup- .plyandwasteiypaaeontolcomfletherei'onthe relativeapproachandrecessioncltheelementsot whichgovernthesaldvalvemechanlam,oneelementotwhichcoupleiemovedproporflonatelyto movement of said valve. the relative position 0! saldelementsbeingturthercontrolled by amotor;

a second control couple, the relative approach and recession of the elements of which govern the supplyof energyto'said latter motor, andmeans responsivetothefluctuatlonsoiavariableoonv dition for relatively positioning the elements of said second couple. v

5. Apparatus for positioning a movable member in accordance with the position 0! a condi tion responsive member comprising, in combination,amotortormovingthemovable member.

tomovethemovablemembertoandtomaintain itatdesiredpositionsundervaryim'advcsecmdiflmsotn'mtion-andthemathmttlingcm 'asomceoi'fluidunderpressurccapabieoi inrnishlnzsaidmotorwiththepowernecessau h'nlvalvetorccntrollmgthesupplydfluidpreosuretothemotorinaeeordanoewiththeoperative positionoisakieontrdvalvmmamlncludmga control valve in acoordmee withthe motive valueoisaideouplanidvalmbelngrktermined bythepositionotsaidconditimrespomivemn-f berand theposition otsaid movablcmemhagand said couple havingarelaflvelysmallthrottling rangeascomparedwlththethrottlingrangect saidcontrolvalvewherebythepowerissuwlied to said motor'necessary to'movethe valve to andmaintainitinposiiionsinaccordancewith thepositionoisaidcondition rmponsive member.

6.Inmechanismiorcontrollingthefiowoi energy governing a motor which exem a force on a movable member proportional at all times to said fiow oi energy, apparatus ior operating said motor to position said movable member in proportional correspondence with a predetermined force value comprising first control means i'rictionlessly changeable in position in proportional correspondence with change in the value oi said predetermined force, second control means changeable in position in proportional correspondence with the position of said movable member, acontrol couple for controlling the flow of energy, said first and second control means so governing said control couple that the force exerted by said motor on said movable member is v proportional to the relative positions of said first v and second control means over a narrow range of relative positions and is maximum for relative positions outside one end oi said narrow range and minimum 'ior relative positions outside the other end 01 said narrow range whereby said second control means and said movable member are caused to assume positions in substantial correforce value.

spondenee with chaste in said I. In apparatus ior controlling the supply of air to a pneumatic motor operating against spring means to position a movable member, mechanism the value of said predetermined iorce, third con-' trol means positionable in proportional correspondence with the position of said movable memher. said second and third means relatively positioning said elements. whereby movement of said second control means by said predetermined iorce causes said third control means to follow withinthelimitofthethrottlingrange oi'said control couple.

mosnmsms'ron 2a 

